Abstract

Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by a loss of substantia nigra pars compacta (SNpc) dopaminergic (DA) neurons, and can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Both inflammatory processes and oxidative stress may contribute to MPTP- and PD-related neurodegeneration. However, whether inflammation may cause oxidative damage in MPTP and PD is unknown. Here we show that NADPH-oxidase, the main reactive oxygen species (ROS)-producing enzyme during inflammation, is up-regulated in SNpc of human PD and MPTP mice. These changes coincide with the local production of ROS, microglial activation, and DA neuronal loss seen after MPTP injections. Mutant mice defective in NADPH-oxidase exhibit less SNpc DA neuronal loss and protein oxidation than their WT littermates after MPTP injections. We show that extracellular ROS are a main determinant in inflammation-mediated DA neurotoxicity in the MPTP model of PD. This study supports a critical role for NADPH-oxidase in the pathogenesis of PD and suggests that targeting this enzyme or enhancing extracellular antioxidants may provide novel therapies for PD.

Ethidium fluorescence (A) and Mac-1 immunostaining (B) are minimal in the saline-treated mice. By 2 days after MPTP injections, SNpc ethidium fluorescence is increased in WT mice (C) and is absent in gp91phox-deficient mice (E) and minocycline-treated WT mice (G). Microglial activation is prevented by minocycline (H) but is normal in gp91phox-deficient mice (E). MPTP stimulates NADPH-oxidase activation, as evidenced by p67phox translocation from the cytosol to the plasma membrane in WT mice (wt), but not in gp91phox-deficient mice (ko) (I and J); the membrane protein calnexin is used to normalize the data. Data are means ± SEM for four to six samples per group. *, P < 0.05, higher than controls; #, P < 0.05, less than MPTP-injected WT mice, but not different from both saline-injected groups.

(A) Ventral midbrain carbonyl content, used as a marker of protein oxidative damage, is increased at 2 days after MPTP injections in WT mice (wt), but not in gp91phox-deficient mice (ko). Infusion of SOD1 into the left striatum attenuates the striatal (B) and the SNpc lesion on the infused side, but not on the contralateral, noninfused side (C) after a systemic injection of MPTP. *, P < 0.05, higher than controls; #, P < 0.05, less than MPTP-injected WT mice, but not different from the two saline-injected groups.